1. Field of the Invention
This invention relates to the field of electrical connectors, and in particular to a current-mode coupler capable of non-invasively transferring electronic data signals to and from a twisted pair cable.
2. Description of Related Art
Couplers for sensing the transmission of low-level signal currents through an electrical conductor without an electrical connection to the conductor, thereby eliminating the need for direct wiring into the bus cable, have recently been developed for use in environments such as aircraft in which replaceable couplings, for example of black boxes and other electronic control units with a single closed loop data bus, are required.
The present invention is an improvement on the coupler disclosed in U.S. Pat. No. 4,904,879. The device disclosed in U.S. Pat. No. 4,904,879 is a coupler assembly for establishing a non-invasive coupling to the conductor wires of a twisted pair data bus cable in which mating pairs of E-shaped electromagnets are arranged to define a pair of electromagnetic cores having windings about central legs thereof which are electrically connected to a control unit for sensing and transmitting signals along the data bus. The coupler assembly of U.S. Pat. No. 4,904,879, designed for use in aircraft, includes an upper half and a lower half connected together by a pivot at one end and a quarter turn latch at the other. The lower E-cores are molded into an insulating unit, which is coated with elastomeric material both between the cores and external to the cores for respectively holding the wires in place and providing a biasing force to ensure that the upper and lower E-cores mate properly without an air gap. A circuit board module in the pivotal upper half of the coupler assembly is separately shielded by a metallic housing which is soldered onto the circuit board substrate. Assembly is accomplished by bolting the lower half to a frame, inserting the data bus cable wires, and pivoting the upper half to cause the E-cores to mate with each other.
Although this type of current mode coupler possibly presents an improvement over prior devices, a number of disadvantages remain. These include inadequate coupling between the E-cores and the data bus cable wires, a higher than optimum write winding current requirement, and the tendency of the elastomeric core suspension to deteriorate over time, resulting in formation of an air gap and thereby increasing the reactance of the core structure. In addition, the simple bolt and nut mounting arrangement used for mounting the lower half of conventional non-invasive data bus couplers to a panel, and the relatively complex pivoting structure required to attach the upper coupler half to the lower half present problems in situations where the coupler is to be mounted in a relatively inaccessible area. The fact that the prior coupler provides no arrangement for shielding the core assembly could also present problems, although the signal amplifiers themselves are shielded. Finally, the coupler of U.S. Pat. No. 4,904,879, due to its high current requirements and geometric design, may be subject to overheating.
Therefore, even though the desirability of the basic concept of the non-invasive data current has previously been recognized, an optimal arrangement from the standpoint of both operational life and convenience has yet to be achieved.